If you are looking to change the salutation in a Quote email for Cart2Quote to be First Name instead of full name you can change the following

<p class="greeting">{{trans "Hello %customer_name," customer_name=$quote.getCustomerName()}}</p>


<p class="greeting">{{trans "Hello %customer_name," customer_name=$quote.getCustomerFirstname()}}</p>

nb. It is important to note that Firstname and FirstName are not the same and FirstName will not work. Make sure you do not capitalise the n.

More useful resources here: https://cart2quote.zendesk.com/hc/en-us/articles/201151179--DEV-How-to-change-address-in-the-email-templates-